Fulminating material application technique

ABSTRACT

A METHOD OF APPLYING FULMINATING MATERIAL ON THE PRIMER ANVIL WIRE OF A PERCUSSIVE-TYPE PHOTOFLASH LAMP IN WHICH: THE ANVIL WIRE IS DIPPED INTO AN AQUEOUS SLURRY CONTAINING RED PHOSPHORUS TO PROVIDE A COATING THEREOF ON THE WIRE; THE COATING IS DRIED; AND THEN THE COATED WIRE IS DIPPED INTO AN AQUEOUS SOLUTION OF SODIUM CHLORATE SO AS TO PERMEATE THE PHOSPHORUS CONTAINING COATING WITH THE CHLORATE SOLUTION.

June 6, 1972 s v, BROWN EIAL FULMINATING MATERIAL APPLICATION TECHNIQUE Filed Oct. 22, 1970 m K N W N mwS mw m B cFT T MMN N V E E v G E W A HA WWW Y THO B ST United States Patent 3,667,992 FULMINATING MATERIAL APPLICATION TECHNIQUE Stephen V. Brown, Williamsport, Thomas B. McDonough, Alleuwood, and John W. Shatter, Williamsport, Pa., assignors to Sylvania Electric Products Inc. Filed Oct. 22, 1970, Ser. No. 83,135 Int. Cl. B44d 1/14 U.S. Cl. 117-69 8 Claims ABSTRACT OF THE DISCLOSURE A method of applying fulminating material on the primer anvil wire of a percussive-type photofiash lamp in which: the anvil wire is dipped into an aqueous slurry containing red phosphorus to provide a coating thereof on the wire; the coating is dried; and then the coated wire is dipped into an aqueous solution of sodium chlorate so as to permeate the phosphorus containing coating with the chlorate solution.

The invention relates to the manufacture of photofiash lamps and more particularly to those of the percussive type.

Generally speaking, a percussive-type photofiash lamp comprises an hermetically sealed, light-transmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussivetype photofiash lamp comprises a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible, such as shredded zirconium foil, and a combustion supporting gas, such as oxygen. The primer comprises a metal tube and a charge of fulminating material on a wire anvil supported therein. Operation of the lamp is initiated by an impact onto the tube of the primer to cause deflagration of the fulminating material on the wire anvil up through the tube to ignite the combustible disposed in the lamp envelope.

The requirements that must be met by a fulminating material for percussive fiashlamps are unique and differ appreciably from those for the filament-initiated paste used in battery operated flashlamps. These differences arise primarily from the percussive mode of initiation and the extreme mechanical sensitivity required therefor. In battery operated flashlamps, the ignition paste is heated by a wire filament until ignition occurs. Energy input to the paste extends over a period of one or more milliseconds. In contrast, energy input to the fulminating material of a percussive flashlamp is in the form of a single nearly instantaneous impact, the duration of which would be measured in microseconds. The impact energy available is severely limited by mechanical size restrictions, the necessity for vibration-free operation, and the need to synchronize the lamp with the operation of a delicate and precise camera shutter mechanism. Accordingly, the fulminating material for percussive flashlamps must be extremely sensitive. This necessary sensitivity has been achieved by the use of an intimate mixture of red phosphorus and potassium chlorate along with a finely powdered metal such as titanium.

Ignition pastes for conventional filament type flashlamps use nitrocellulose as a binding resin, and organic solvents such as amyl acetate as the vehicle. In an effort to increase the handling safety of percussive fulminating material, water was evaluated as the vehicle in conjunction with water soluble binding resins such as hydroxyethyl cellulose. The fulminating material deposited from such an aqueous suspension was found to be much more sensi- 3,667,992 Patented June 6, 1972 "ice tive to impact than a similar material deposited from organic solvents. This enhanced sensitivity was attributed to deposition of the potassium chlorate onto the particles of red phosphorus, resulting in a more intimate mixture. Although these gains in lamp sensitivity and reliability were significant, the new water-based fulminating materials were found to retain a degree of hazard. It was found, for example, that a crust of dried material generated enough heat during flashing to ignite the adjacent aqueous fluid, and that the latter would burn to completion. The burning violence of the wet material varied inversely with the amount of water present.

Accidental drying or partial drying of the sensitive fulminating material constituted an ever present danger of fire or explosion in the production process. In order to restrict the danger involved in handling and using the fulminating material, it was prepared in small batches. The amount allowed in any one container was limited to a fraction of an ounce of solid ingredients. The high cost of preparing numerous small batches was completely overshadowed by the lost machine production time required for frequent replacement or refilling of the small fulminating material dip cups.

In an effort to avoid the use of such hazardous materials in production, a two-layer technique for applying fulminating material was evaluated in which the potassium chlorate and red phosphorus were not mixed. In this technique, separate coatings of potassium chlorate and of red phosphorus-metal mixture were applied one over the other. Each component was prepared as a milled aqueous slurry containing the chosen ingredients along with a quantity of binding resin. It was found that application of the red phosphorus-containing layer over a layer containing potassium chlorate was preferable to applying the oxidizer layer last. However, extensive testing and effort failed to attain the degree of lamp reliability and photometric performance with this two layer system that had been achieved with the aqueous completely mixed material. The shortcoming of such two-layer structures is that only single surface-contact exists between the red phosphorus and potassium chlorate, whereas in completely mixed material intimate bulk contact is attained.

In view of the foregoing, the principal object of this invention is to provide a method of applying fulminating material on the primer anvil wire of a percussive type photofiash lamp which is safe and economical for large scale production and at the same time provides an impact sensitivity such that the fiashlamps will have a high degree of ignition reliability and photometric performance.

It has been found that the high solubility of sodium chlorate makes a safe and completely different technique of fulminating material application possible. A coating of red phosphorus and titanium is applied to the anvil and dried. This coating is then permeated with sodium chlorate by dipping into an aqueous solution containing about 20% sodium chlorate by weight. As the concentrated solution of sodium chlorate penetrates the interstices of the red phosphorus containing layer, a degree of intimacy comparable to that obtained with completely mixed waterbased fulminating material is realized. Impact sensitivity, lamp reliability, and lamp light output characteristics compare favorably with performance obtained with the best completely mixed fulminating material.

Sodium chlorate is not generally used in impact sensitive mixtures because it absorbs moisture which results in deactivation. It can be used to advantage in the fulminating material for percussive flashlamps, however, due to the hermetically sealed structure of such lamps.

An example of a very satisfactory system using the principles of this invention is given below.

The anvil is first dipped into an aqueous slurry having the following dried composition: titanium, 70.49%; red

phosphorus, 22.58%; hydroxyethyl cellulose 4.35%; sodium lignin sulfonate, 1.70%; magnesium oxide, 0.64%; sodium 2-ethylhexyl sulfate, 0.11%; sulfur, 0.06%; and trichlorophenol, 0.06%. The water content is adjusted to give the desired coating thickness. This coating is then dried and dipped into an aqueous solution containing 19% by weight of dissolved sodium chlorate. Upon drying, a very sensitive fulminating material coating results.

The burning behavior of the dried residue prepared as described above, varies greatly with the concentration of sodium chlorate used. Below about by weight sodium chlorate in the dip solution, impact sensitivity falls off rapidly. A saturated solution containing about 52% sodium chlorate by weight may be used but the resulting coating burns violently and results in a decreased light output from the flashlamp. Other chlorate salts of high solubility (e.g. soluble to the extent of or greater by weight in Water) may be used, for example calcium chlorate, lithium chlorate, magnesium chlorate, aluminum chlorate, and zinc chlorate. However, the extreme deliquescence of these materials may render their use in flashlamps more diificult with regard to drying and maintaining the coating dry prior to hermetic closure of the fiashlamp. Similarly, phosphorus sesquisulfide may be used in place of red phosphorus, if desired, although a slight loss in sensitivity may be noted.

In the accompanying drawing, the single figure is a sectional elevational view of a percussive-type photoflash lamp having a primer of the type with which the method of this invention may be employed. The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about a primer 8 at the other end thereof. The primer 8 comprises a metal tube 10 and a wire anvil 12 coated with a charge of fulminating material 14. A combustible such as filamentary zirconium 16 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 on the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial Within the primer tube 10 and insuring clearance between the fulminating material 14 and the inside wall of the tube 10. A refractory bead 24, fused to the Wire anvil 12 just above the inner mouth of the primer tube 10, eliminates bum-through and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer.

Use of the method of this invention makes possible a degree of manufacturing safety never before approached in the production of percussive flashlamps. As the red phosphorus containing slurry is quite innocuous in the absence of oxidizers, larger volume slurry dip cups can be safely used with attendant manufacturing equipment efiiciency. High sensitivity and lamp reliability are readily attained along with dependably uniform performance.

What we claim is:

1. The method of applying fulminating material on a primer anvil wire of a percussive-type photoflash lamp, said method comprising:

applying a phosphorus containing coating on said wire;

drying said coated wire;

and permeating said phosphorus containing coating with a chlorate salt solution.

2. The method of claim 1 in which said chlorate salt solution is an aqueous solution containing at least 15% by weight of dissolved chlorate salt.

3. The method of claim 1 in which said chlorate salt solution is an aqueous solution containing not less than 10% and not more than 52% by weight of dissolved sodium chlorate. I

4. The method of claim 1 in which the last step is performed by dipping said coated wire into said chlorate salt solution.

5. The method of claim 2 in which the coating applied to said wire contains red phosphorus.

6. The method of claim 2 in which the coating applied to said wire is an aqueous slurry containing red phosphorus and titanium.

7. The method of claim 3 in which the first step is performed by dipping said Wire into an aqueous slurry having a dried composition of titanium, red phosphorus, hydroxyethyl cellulose, sodium lignin sulfonate, magnesium oxide, sodium 2-ethylhexyl sulfate, sulfur, and trichlorophenol.

8. The method of claim 7 in which the last step is performed by dipping said coated wire into an aqueous solution containing about 20% by weight of dissolved sodium chlorate.

References Cited UNITED STATES PATENTS 2,361,495 10/1944 Pipkin 149-16 3,540,820 11/1970 Shaflicr et a1 431-93 2,431,162 11/1947 Blake et al. 43195 3,535,064 10/ 1970 Anderson et a1 431-93 ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner US. Cl. X.R. 

